Rút gọn các phân thức sau 1, x – 25 / x^2 -10x + 25 2, -x^2 + 2x -1 / x^2 – x 3, 16 – x / -x^2 + 4x 4, 4 – 4x + x^2 / -x^2 + 2x

`1. (x^2-25)/(x^2-10x+25)`

`= [(x-5)(x+5)]/(x-5)^2`

`= (x+5)/(x-5)`

`2. (-x^2+2x-1)/(x^2-x)`

`= -(x-1)^2/[x(x-1)]`

`= (-x+1)/x`

`3. (16-x^2)/(-x^2+4x)`

`= [(4-x)(4+x)]/[x(4-x)]`

`= (x+4)/x`

`4. (4-4x+x^2)/(-x^2+2x)`

`= (x-2)^2/[-x(x-2)]`

`=- (x-2)/x`